Context : The chemically peculiar ( CP ) stars of the upper main sequence are mainly characterized by strong overabundances of heavy elements .
Two subgroups ( CP2 and CP4 ) have strong local magnetic fields which make them interesting targets for astrophysical studies .
This star group , in general , is often used for the analysis of stellar formation and evolution in the context of diffusion as well as meridional circulation .

Aims : In continuation of a long term study of CP stars ( initiated in the 1980ies ) , we present new results based on photoelectric measurements for ten open clusters that are , with one exception , younger than 235 Myr .
Observations in star clusters are favourable because they represent samples of stars of constant age and homogeneous chemical composition .

Methods : The very efficient tool of \Delta a photometry was applied .
It samples the flux depression at 5200Å typically for CP stars .
In addition , it is able to trace emission line Be/Ae and \lambda Bootis stars .
Virtually all CP2 and CP4 stars can be detected via this tool , and it has been successfully applied even in the Large Magellanic Cloud .
For all targets in the cluster areas , we performed a kinematic membership analysis .

Results : We obtained new photoelectric \Delta a photometry of 304 stars from which 207 objects have a membership probability higher than 50 % .
Our search for chemically peculiar objects results in fifteen detections .
The stars have masses between 1.7 M _ { \sun } and 7.7 M _ { \sun } and are between the zero- and terminal-age-main-sequence .
We discuss the published spectral classifications in the light of our \Delta a photometry and identify several misclassified CP stars .
We are also able to establish and support the nature of known bona fide CP candidates .

Conclusions : It is vital to use kinematic data for the membership determination and also to compare published spectral types with other data , such as \Delta a photometry .
There are no doubts about the accuracy of photoelectric measurements , especially for stars brighter than 10th magnitude .
The new and confirmed CP stars are interesting targets for spectroscopic follow-up observations to put constraints on the formation and evolution of CP stars .